Estimation of Daily Solar Radiation from Measured Air Temperature Extremes in the Mid-Mediterranean Area

AbstractDaily solar radiation Rs at ground level is a necessary input variable required for the evaluation of evapotranspiration and crop growth, development, and yield-simulation models. Nevertheless, it is measured in few weather stations and at many locations it is not observed; also, available Rs temporal series are generally no longer than a few years. A valid surrogate of Rs measurement is the diurnal air-temperature range (ΔT); indeed, ΔT is inversely proportional to cloudiness and therefore could be a good indicator of atmospheric transmittance. As opposed to Rs, daily maximum and minimum air temperatures are measured at many locations and their observations in developed countries began in the 19th century. For this reason, several models that permit Rs indirect evaluation from air-temperature data have been suggested in the literature. The most famous models are the simple Hargreaves-Samani (HS) formula, many times recalibrated by the authors, and the Bristow-Campbell model, which has recently be...